Electrostatic powder sprayer



W. G. BUHLER ELECTROSTATIC POWDER SPRAYER Sept. 26, 1967 6 Sheets-Sheet1 Original Filed April 23, 1964 A T TORNEYS m mi J m Q N ,1 E

6 Sheets-Sheet 2,v

ATTORNEY:

Sept. 26, 1967 w. G. BUHLER ELECTROSTATIC POWDER SPRAYER Original FiledApril 23, 1964 P 1967 w. G.BUHLER ELECTROSTATIC POWDER SPRAYER 6Sheets-Sheet 5 Original Filed April 23, 1964 FIG. 5

FIG 6 IN VEN TOR. WARREN G. BUHLER M ATTORNEYS P 26, 1967 w. cs. BUHLERELECTROSTATIC POWDER SPRAYER 6 Sheets5heet 4 Original Filed April 23,1964 V INVENTOR. WARREN a. BUHLER [[IIIIII I I ll I Ill ,arronweys Sept.26, 1967 w. G. BUHLER ELECTROSTATIC POWDER SPRAYER e Sheet-Sheet 5Original Filed April 25, 1964 0 000 O0 0 00 o 00 0 co co IN VEN TOR.WARREN G- BUHLER &MZ z/Z'e A TTOENEYS Sept. 26, 1967 w. G. BUHLER3,344,312

ELECTROSTATIC POWDER SPRAYER Original Filed April 23, 1964 sSheets-Sheet 6 nvmvroa 97 WARREN a. BUHLER A TTORNE Y5v United StatesPatent 3,344,312 ELECTROSTATIC POWDER SPRAYER Warren G. Bnhler,Westfield, NJL, assignor to Oxy-Dry Sprayer Corporation, New York, N.Y.,a corporation of New York Original application Apr. 23, 1964, Ser. No.362,106, now Patent No. 3,292,045. Divided and this application Aug. 15,1966, Ser. No. 572,571

3 Claims. (Cl. 3172) ABSTRACT OF THE DISCLOSURE A powder sprayer,including a powder receptacle, with a dispensing roller and associatedwiping blades forming a mechanism for metering powder from thereceptacle. A pair of A.C. electrostatic tubes are located closelyadjacent the dispensing roller and on opposite sides of the meteringmechanism. A pneumatic structure provides an air curtain on each side ofthe metering mechanism to confine the dispensed powder to the desiredarea.

This invention relates to electrostatic powder sprayers, and moreparticularly to powder sprayers capable of laying down a substantiallyuniform layer of fine powder material. This application includes subjectmatter common with copending application Serial No. 362,106 filed Apr.23, 1964, now Patent 3,292,045.

The prior electrostatic powder sprayers have usually included a powderbox, a metering mechanism for dispensing powder material from the powderbox at a substantially uniform rate, and apparatus for providing anelectrostatic field to free powder particles from the metering mechanismand to disperse the powder particles. Typically, the electrostatic fieldwould be created by a single gas filled discharge tube secured in afixed position relative to the metering mechanism. Substantial successhas been achieved with these prior units when designed to dispense aparticular type of powder material with a limited range of dispensingrates.

An object of this invention is to provide an electrostatic powdersprayer capable of dispensing a wide variety of powder materials withoutany significant limitation upon the available dispensing rates.

Another object of the invention is to provide a powder sprayer which isadjustable so as to vary the field pattern and strength of theelectrostatic field used to free the powder particles from the meteringmechanism and to disperse the powder particles.

Still another object is to provide an electrostatic powder sprayer whichcan be adjusted to provide symmetrical or non-symmetrical electrostaticfields so as to control the downward direction of falling powderparticles.

Another object is to provide an electrostatic powder sprayer wherein thedischarge tubes utilized to create the electrostatic field aredetachably secured and easily replaced.

The manner in which the foregoing and other objects are achieved is setforth more fully in the following specification which describes a fewillustrative embodiments within the scope of this invention. Thedrawings form a part of this specification wherein:

FIG. 1 is a perspective view, with portions broken away, illustratingone end of the powder syrayer;

FIG. 2 is a perspective view illustrating the other end of the powdersprayer with the journal structure partially disassembled;

FIG. 3 is a plan view of the powder sprayer and associated drivingmechanism;

FIG. 4 is a side view of the powder sprayer;

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FIG. 5 is an end view of the powder sprayer taken along line 55 asindicated in FIG. 4;

FIG. 6 is a cross sectional view of the powder sprayer taken along line6-6 as indicated in FIG. 4;

FIG. 7 is a longitudinal cross sectional view of the powder sprayerillustrating the journal structure and taken along line 7-7 as indicatedin FIG. 3;

FIG. 8 is an enlarged partial cross sectional view of the structureshown in FIG. 6 illustrating the details of the Wiping blade assembly;

FIG. 9 is an illustration of the roller surface in accordance with oneembodiment of the invention as seen from line 99 in FIG. 8;

FIG. 10 is an illustration of an alternative surface structure for theroller as seen along line 99 in FIG. 8;

FIG. 11 is a cross sectional view illustrating the socket structure forretaining one end of a discharge tube; and

FIGS. 12 and 13 are cross sectional views of one of the end bracketstaken along line 1212 in FIG. 4 and illustrating the adjustabledischarge tube support structure.

General description The powder sprayer in accordance with this inventionincludes a dispensing roller and a pair of wiping blades whichtangentially engage the dispensing roller on opposite sides. As theroller rotates, powder is dispensed at a substantially uniform rate froma powder box located above the dispensing roller. A separateelectrostatic discharge tube is positionable beneath each of the wipingblades. Each of these discharge tubes is detachably secured between aspring biased socket at one end and a rigid socket at the other end. Adischarge tube is inserted by first forcing one end into the springbiased socket, thereby compressing a spring within the socket, and bythereafter releasing the discharge tube so that the other end isretained in the rigid socket by means of spring pressure. The dischargetube is easily removed by moving the tube longitudinally to againcompress the spring, and by then removing the discharge tube from therigid socket.

The end portions of the receptacle forming the powder box areconstructed to provide arcuate surfaces which are eccentric with respectto the cylindrical surface of the dispensing roller. A pair of arcuatesupport brackets are attached to slidably engage these arcuate surfacesand are constructed to provide pivotable support for the sockets whichengage the ends of the discharge tubes. Thus, the discharge tubes can beplaced in virtually any desired position parallel to the dispensingroller because of the double adjustments achieved by means of thepivotable and slidable support structure. By varying the position of thedischarge tubes, the electrostatic field pattern and the strength of theelectrostatic field can be varied as desired. As a result, theelectrostatic powder sprayer can be adjusted for a wide variety ofpowder materials and operating conditions.

Powder box, wiper blades and air curtain First, referring to FIGS. 1-13,an advantageous embodiment of the invention is illustrated wherein thepowder sprayer includes a powder box 1, defined by a pair of spacedapart side panels 2 and 3, end brackets 4 and 5 and a dispensing roller11. The side panels are secured between the end brackets by means of twopairs of support blocks 9 and 10, these support blocks being formed asan integral portion of the end brackets. The side panels are secured tothe support blocks by means of suitable screws as illustrated. A spacermember 12 is secured intermediate the ends of the side panels and isflush with the upper edge thereof. A lid 6 is secured to the upper edgeof side panel 2 by means of a hinge 9 and is dimensioned to cover thetop of the powder box and wrap over the upper edge of side panel 3 whenin the closed position. Dispensing roller 11 is journaled in the endbrackets and is disposed between the lower edges of side panels 2 and 3.

The side panels, best seen in FIGS. 1, 6 and 8, are preferably integralextruded aluminum panels. Side panel 3 includes a vertical outer portion14, a sloping portion and a lower horizontal portion 16, which portionsdefine a plenum chamber 17 having a generally triangular cross sectionand extending through the side panel from end to end. The slopingsurface 15 lies in a plane tangential to dispensing roller 11 and meetsvertical portion 13 somewhat below the upper edge of the side panel.Surface 15 extends beyond the horizontal portion 16 and forms onesurface of a lower extended portion 18. The other fiat surface ofextended portion 18 is a blade retaining surface 19 which lies in aplane which meets the plane of surface 15 at the point of tangency withthe roller, or somewhat below the point of tangency. The right dihedralangle between these planes is approximately 20 degrees. The lower edgeof extended portion 18 is rounded as shown.

A longitudinal V-shaped groove 25, best seen in FIG. 8, is machined intothe lower surface of horizontal portion 16. This groove forms an outervertical groove surface 26 and inwardly sloping groove surface 27.Preferably, the groove is located directly below the outer portion ofplenum chamber 17. A plurality of holes 28 are drilled through bottomportion 16 extending between the apex of groove and plenum chamber 17.

When the side panel is secured in position, end bracket 4 seals off oneend of plenum chamber 17, and end bracket 5 seals off the other end. Ahose connecting nipple 29 is threaded into a threaded bore 30 passingthrough end bracket 4 so as to communicate with plenum chamber 17. Asuitable air pump can be coupled to the plenum chamber via an air hose(not shown) to create a pneumatic pressure within the chamber. As aresult, a plurality of air jets are formed via holes 28. Because ofgrooves 25, these jets tend to fan out elliptically and thus provide arelatively uniform air curtain extending between adjacent holesthroughout the entire length of the side panel. Due to sloping groovesurface 27, a portion of each of these jets is directed inwardly toprevent accumulation of powder on retaining member 20, adjusting screws22 and wiping blade 23 located beneath the side panel.

Side panel 2 is identical to side panel 3 and includes components 33-49corresponding, respectively, to components 13-29 of side panel 3. Asshown in FIG. 6, the end bracket 4 seals off one end of plenum chamber17, and end bracket 5 seals off the other end. Preferably, a sealinggasket is cemented in position between the end brackets and the sidepanels. A hose connecting nipple 29 is threaded into a threaded bore 30passing, through end bracket 4 so as to communicate with plenum chamber17. A suitable air pump can be coupled to the plenum chamber via an airhose (not shown) to create a pneumatic pressure within the chamber. As aresult, a plurality of air jets are formed via holes 28. Because ofgroove 25, these jets tend to fan out elliptically and thus provide arelatively uniform air curtain extending between adjacent holesthroughout the entire length of the side panel. Due to sloping groovesurface 27, a portion of each of these jets is directed inwardly toprevent accumulation of powder on retaining member 20, adjusting screws22 and wiping blade 23 located beneath the side panel.

Side panel 2 is identical to side panel 3 and includes components 33-49corresponding, respectively, to components 13-29 of side panel 3. Asshown in FIG. 6, the powder material to be dispensed is placed in thepowder box between sloping surfaces 15 and 35 and above dispensingroller 11. Thus, the sloping surfaces serve to funnel the powderdownwardly toward the dispensing roller. It should be noted that theplenum chambers are therefore located in an area which would otherwisebe wasted space. Plenum chambers 17 and 37 are sufiiciently large sothat the air pressure therein is substantially uniform over the entirelength of the side panels.

Wiping blades 23 and 43 are each constructed from a thin, flexible stripof blue spring steel and are preferably coated with a fluorocarbonmaterial. These blades are approximately one inch wide and have a lengthequal to the length of side panels 2 and 3. Holes are drilled throughthe blade near the upper edge and are spaced on two inch centers.

Semi-rigid retaining member 20, best seen in FIG. 8, is preferably anextruded aluminum strip equal in length to wiping blade 23 and sidepanel 3. Longitudinally spaced holes are drilled through retainingmember 20 corresponding in position to the holes in blade 23, andcorresponding tapped holes are drilled into extended portion 18 of sidepanel 3, these holes being normal to blade retaining surface 19. Wipingblade 23 is positioned between extended portion 18 of the side panel andretaining member 23 and this assembly is secured by means of suitableround head adjusting screws 22. Preferably, the holes in the wipingblade, retaining member and extended portion of the side panel areaccurately aligned so that the wiping blade can easily be replaced.

Retaining member 20 includes a flat blade engaging surface which curvesinto an inwardly extending rib 21 at the lower edge thereof. Thedistance between screw 22 and rib 21 must be greater than the distancebetween screw 22 and the lower edge of extended portion 18. The distancebetween screw 22 and the upper edge 24 of the retaining member ispreferably somewhat greater than the distance along surface 19 betweenscrew 22 and the lower surface of bottom portion 16. Thus, when thescrew 22 is tightened, moving retaining member 20 toward retainingsurface 19, the upper edge 24 strikes the lower surface of bottomportion 16. Thereafter, when screw 22 is further tightened, retainingmember 24 pivots about edge 24 and applies pressure along thelongitudinal center line of blade 23 via rib 21. As a result, the bladeis bent inwardly by rib 21 along the center line of the wiping bladewhich is located between extended portion 18 and line of tangency onroller 11. Thus, the wiping blade is laterally deformed and takes on anS-shaped bend as shown in FIG. 8. In this manner, the flexible bladebecomes rigid and substantially straight in the longitudinal direction.Each of the screws 22 are separately adjustable, and hence, the pressureapplied by the wiping blade against dispensing roller 11 can be adjustedas desired at selected points along the blade. This permits adjustmentsto compensate for uneven wear or for tolerances in the dispensing rollersurface or the side panel. Also, it is possible to adjust the blade sothat greater pressure is exerted against the dispensing roller inselected areas to thereby obtain a non-uniform dispensing rate whendesired.

End brackets and discharge tube mounting structure End brackets 4 and 5are identical to one another and are secured abutting the ends of sidepanels 2 and 3 by means of support blocks 9 and 10 respectively Whichform integral portions of the end brackets. The end brackets thus serveas closure members for the ends of the powder box and the ends of theplenum chambers within the side panels. Also, the end brackets supportbearings for the journals for dispensing roller 11, arcuate surfaces forcooperating with the discharge tube supporting structure, and bracketportions for securing the powder sprayer, to associated apparatus or asuitable support frame struc ture.

End bracket 4 is an integral structure including an end closure member60, a substantial circular boss 61 extending horizontally away from thesurface of closure member, and a support leg 6-2 extending horizontallyfrom the flat surface of the boss. The diameter of circular boss 61 isapproximately equal to the distance between the outer surfaces of sidewalls 2 and 3. Boss 61 is positioned to accommodate an off-centerjournal housing 63 for discharge roller 11, the discharge roller beinglocated as shown in FIG. 12. The lower portion of closure member 60,i.e., the portion lying below the horizontal center line of boss 61, iscurved and conforms to the circular configuration of the boss. Supportblocks 9 are secured to the edges of closure member 60 and extend in thedirection of the side panels. Support blocks 9 are spaced apart so thatthey will lie on the outer surfaces of the side panels when the endbracket is secured in position. The upper edges of closure member 60 andboss 61 are flush with the upper edges of side panels 2 and 3.

Support leg 62 can have any desired configuration and includes a pair ofslots 64 and 65 therein extending through the support leg from top tobottom. As shown in FIG. 7, support leg 62 is positioned slightly belowthe upper surface of boss 61 and is strengthened by means of a taperedrib 66 extending from boss 61 along the upper surface of the supportleg. The support leg can be either horizontal as shown, or can bevertical to facilitate side mounting.

End support bracket 5 is an integral structure identical to end supportbracket 4 and includes an end closure member 70, a substantiallycircular boss 71, a pair of spaced apart support blocks 10, and asupport leg 72 with an associated strengthening rib 76 and slots 74 and75. Thus, when the end brackets are secured in the positions as shown inFIGS. 1 and 2, the brackets close the ends of the powder box and alsoclose the ends of the plenum chambers within the side panels. Preferablya sealing gasket is cemented in position between the end brackets andthe ends of the side panels. As previously mentioned, a pair of bores 30and 50 are provided extending through end bracket 4 and are eachpositioned to communicate with a different one of the plenum chambers 17and 37 respectively. The threaded bores are adapted to accommodatethreaded hose connecting nipples 29 and 39 respectively. End bracket 5likewise includes a pair of threaded bores so that this end bracket willbe identical to end bracket 4. The threaded bores in end bracket 5,however, are not used and are therefore sealed by means of suitablethreaded plugs 77 and 78. The assembled powder sprayer can be positionedas desired by means of suitable bracket members (not shown) bolted tosupport legs 62 and 72 or by bolting the support legs directly to asuitable supporting structure.

Discharge tubes 80 and 81 are similarly constructed and each include acylindrical glass tube which is evacuated and then filled with an inertgas such as argon. The glass tubes are slightly longer than the sidepanels and are internally coated with a suitable phosphorous material.The discharge tubes include a cathode at one end only. As shown in FIG.11, the cathode end of the discharge tube includes a cup shaped cathodemember 82 connected to a conductive metallic end cap 83 by means of asuitable support conductor 84.

It is desirable that the discharge tubes be positioned generallyparallel to dispensing roller 11 and that they be adjustable in positionwith respect to the roller. Also, it is desirable that the tubes bedetachably secured so that they can easily be replaced.

The discharge tube support structure for tube 81 includes a support arm90 having an arcuate inner surface with the same radius of curvature asthe arcuate surface 91 at the periphery of boss 61. Thus, the innersurface of support arm 90 is adapted to engage arcuate surface 91 asshown in FIG. 1, and is adjustable with respect to the boss. Support arm90 includes an elongated locking slot 92 including an elongated annularshoulder 93 (best seen in FIGS. 12 and 13) which is concentric with thearcuate surface of boss 61. A tapped hole is bored into boss 61 alongthe horizontal center line and is dimensioned to accommodate a sockettype cap screw 94 which passes through slot 92. Thus, when cap screw 94is loosely placed in position, support arm can slide from an upperposition as shown in FIG. 12 to a lower position shown in FIG. 13. Itshould be noted that arcuate surface 91 is eccentric with respect to thedispensing roller surface due to the off-center location of the jour-'nal housing with respect to boss 61. Support arm 90 can be rigidlysecure at any position by tightening cap screw 94 so that the head ofthe screw engages shoulder 93 of the locking slot.

The lower portion of support arm 90 (as viewed in FIG. 1), is offset andis constructed to provide a bifurcated end portion 95 dimensioned toaccommodate a tab 96 extending from a spring biased tube socket 97. Asshown in FIG. 11, a pair of axially aligned threaded apertures passthrough the leg portions of bifurcated end 95 and a smaller diameter,axially aligned, aperture passes through tab 96. A pair of socket type,headless, set screws 98 and 99 are threaded into the leg portions ofbifurcated end 95 so that the dog point ends of the set screws residewithin the aperture passing through tab 96. In this manner, socket 97 ispivotably secured to support arm 90 (as illustrated in FIG. 13) and canbe rigidly maintained in any desired pivoted position by appropriateadjustment of set screws 98 and 99.

A support arm 100, which is a mirror image of support arm 90, is adaptedto engage the arcuate surface 101 located at the periphery of boss 71 ofend bracket 5. Support arm is secured to end bracket 5 by means of a capscrew 104 which passes through an elongated locking slot 102 and engagesshoulder 103 within the slot. A tab 106 extending from a cup shaped tubesocket 107 is pivotably secured to support arm 100 by means of an offsetbifurcated end portion 105. Tube socket 107 is preferably constructedfrom a material having a high electrical resistance and is dimensionedinternally to accommodate the end of electrostatic tube 81.

Spring biased socket 97 includes a generally cylindrical outer housing110 which is partially closed at one end. An insulated conductor 111passes through the partially closed end of housing 110 and through thecenter of a retaining washer 112. The free end of the conductor isembedded in a globule or head of solder 113 to provide a relativelylarge conductive surface and to prevent conductor 111 from pulling outof the washer. A spring 114 is disposed between retaining washer 112 andthe partially closed end portion of housing 110 to urge the retainingwasher away from the partially closed end of the housing. As previouslymentioned, tab 96, which extends radially from housing 110, is pivotablysecured by the bifurcated end portion of support arm 90. Housing 110 ispreferably an integral structure constructed from a material having ahigh electrical resistance. 7

Conductor 111 after emerging from the end of socket 97, is connected toone end of a high voltage secondary winding 115 of a transformer 116,the other end of the secondary winding being connected to a suitableground, which may be the side panels of the powder sprayer or a groundsurface located at some point below the sprayer. Primary winding 117 oftransformer 116 is connected to a suitable 60 cycle alternating currentsource. Transformer 116 is preferably constructed to provideapproximately 10,000 volts to electrode 82 via conductor 111.

Discharge tube 81 is installed by inserting the electrode end intospring biased socket 97 thereby compressing spring 114. The other end ofthe discharge tube is then inserted into socket 107, and when released,is retained in socket 107 by virtue of the force extended by spring 114.Thereafter, discharge tube 81 can easily be adjusted to any desiredposition parallel to dispensing roller 11 by means of the pivotableconnection between the sockets and support arms 90 and 100, or byadjusting the position of the support arms relative to end brackets 4and 5.

The adjustable support structure for discharge tube 80 is essentiallythe same as the supporting structure for discharge tube 81, except thatit is attached to position tube 80 on the opposite side of dispensingroller 11. The components comprising the adjustable supporting structurefor discharge tube 80 are designated with reference numerals 126-144corresponding respectively to reference numerals 96-114. Conductor 141emerging from socket 127 is also connected to the ungrounded end ofsecondary winding 115 (FIG. 11).

Roller asttembly Roller 11 can be a solid steel roller with longitudinalextending shafts, as shown in the drawings, or can include a hollowcylindrical roller with suitable roller gudgeons secured to the ends toform the longitudinal extending shaft portions. The length of the rollerportion is slightly less than the distance between end brackets 4 and asdetermined by the length of the side panels.

Journal shaft 150, extending from one end of roller 11, passes through ajournal opening 151 in end bracket 5 forming part of journal housing 73,and through a flanged bearing 152 constructed from a suitable bearingmaterial, preferably a fluoro-carbon material. Journal opening 151 isdimensioned to accommodate flanged bearing 152 and includes an annularrecess dimensioned to seat the flange of the bearing. As shown in FIG.2, flanged bearing 152 is slid into position from outside end bracket 5and is thereafter secured to the end bracket by means of set screws 153passing through the flange of the bearing. An annular recess is alsoprovided on the inner side of end bracket 5 surrounding journal opening151, to accommodate a felt washer 154 which provides a journal seal andprevents powder from entering the bearing structure. A collar 155 isslid over the end of shaft 156) and is rigidly secured to the shaft bymeans of a set screw 156. This collar is positioned adjacent bearing 152and prevents longitudinal movement of the roller with respect to the endbracket. A sprocket gear 157 is secured near the end of shaft 150 bymeans of a suitable set screw passing through the hub of the gear. Asshown in FIG. 3, a chain 158 couples sprocket gear 157 to an associatedsprocket gear mounted on the shaft of an electric motor 159. Motor 159is preferably of a variable speed drive type capable of rotating roller11 at speeds ranging from small fractions of one rpm. to fifty rpm.

Journal 63 in end bracket 4 is similar to journal 73 previouslydescribed and includes a flanged bearing 162 secured in a journalopening 161 by means of set screws 163 so that the bearing surroundsshaft 160' extending longitudinally from the end of roller 11. A feltsealing washer 164- is provided surrounding the shaft on the inner sideof end bracket 4, and a collar 165 is secured to shaft 160 adjacentbearing 162 by means of set screws 166.

The cylindrical surface 170 of roller 11 is advantageously coated with afluoro-carbon material and thereafter further processed to provide apowder receptive surface. The processed surface of the roller isillustrated in a magnified view of the roller surface shown in FIG. 9and includes an almost infinite number of powder carrying cavities. Asillustrated in FIG. 8, the powder material in powder box 1 is fed bygravity into the area between roller 11 and wiping blade 23. As theroller rotates, a thin layer of powder wedges past the wiping blade. Thethickness of the powder layer, and hence, the quantity of powderdispensed, depends on the adjustment of screws 22, which in turndetermines the blade pressure against the roller. The minimum rate atwhich powder can be dispensed is determined by the capacity of thepowder carrying cavities and the minimum rotation speed of thedispensing roller. The dispensing rate can be increased by eitherincreasing the rotation speed of the roller or by decreasing the bladepressure against the surface of the dispensing roller.

An alternative surf-ace structure for the dispensing roller isillustrated in FIG. where the cylindrical surface is engraved to presenta uniform waffle-like pattern. This 8 structure increases the capacityof the powder carrying cavities which is desirable where high dispensingrates are required or large powder particles are being dispensed.Preferably, the engraved dispensing roller is coated with a fluorocarbonmaterial. With the dispensing roller surface shown in FIG. 10, thedispensing rate can also be varied by adjusting the speed of rotationfor the dispensing roller and the wiping blade pressure.

Although it has been mentioned that the dispensing rate for a givenroller surface can be adjusted by varying the roller speed and bladepressure, there is a practical limit to these adjustments sinceeventually the powder will begin to sift, that is, the powder will beginto come through in uneven chunks resulting in an uneven and relativelyuncontrolled powder distribution. The maximum dispensing rate for aparticular roller varies in accordance with the type of powder beingdispensed. When a particular roller does not achieve the desireddispensing rate, the roller is replaced with another roller havinglarger powder carrying cavities.

It is significant that the roller and the wiping blades are coated witha fluorocarbon material and that the roller bearings are likewiseconstructed from a fluorocarbon material. The fluorocarbon material usedfor coating the roller and wiping blades is preferably the polymer oftrifluorochloroethylene such as marketed under the brand name Kel-F andcharacterized by the formula (CF CFCl) First, these materials exhibit ahigh chemical resistance so that other materials, such as the powderbeing dispensed, cannot readily adhere to the roller and Wiping bladesurfaces. Second, fluorocarbon materials have substantially a zeromoisture absorption characteristic and therefore reduce the possibilityof moisture contamination of the powder being dispensed. Third, thesematerials have a relatively high compression strength and hence,excellent wear characteristics. This is significant in the bearings, andalso with respect to the roller and wiping blade arrangement which issubjected to the constant rubbing action as the powder material, whichmay be abrasive, passes between the roller and wiping blade. Further,fluorocarbon materials have a high electric resistance and highresistance to electrostatic charges. It should be noted that the steelroller, due to the flanged fluorocarbon bearing and fluorocarbon coatingis electrically isolated and hence, is electrically insulated from theelectrostatic field. If the dispensing roller were not isolated, therewould be some electric charge, from the electrostatic field created bydischarge tubes and 81, which would be carried into the powder box bymeans of the roller and thereby electrostatically contaminate the powdermaterial. This electrostatic contamination would adversely affect thedispensing of the powder material.

Assembly and operation The powder sprayer in accordance with thisinvention is of a generally symmetrical design so as to minimize thenumber of different components. The side panel and wiping blade assemblyon one side of the roller is is identical to the side panel and wipingblade assembly on the other side. The end brackets are identical to oneanother, and the two discharge tubes supporting structures are alsosubstantially identical. This symmetrical construction is alsoadvantageous since the dispensing roller can be rotated in eitherdirection and the entire unit can be installed with either side panelfacing outwardly.

The powder sprayer is installed with the dispensing roller positionedhorizontally, usually less than a foot above the surface to be coatedwith the powder material. Usually, the powder receiving surface is inthe form of a moving web or sheet.

The powder or dusting material to be dispensed is either placed directlyin the powder box above dispensing roller 11 or is supplied by asuitable feed machanism. Thereafter, the drive motor is energized torotate motor 11. The roller, if rotating in a clockwise direction,forces powder past wiping blade 23, in which case wiping blade 43 actsas a seal between the side panel and the other side of the roller. Onthe other hand, if the dispensing roller rotates in a counter-clockwisedirection, wiping blade 43 provides the metering function and wipingblade 23 acts as the seal. In either event, the powder material ismetered out at a uniform rate. Thereafter, the force of gravity and theforce created by the electrostatic field provided by the dischargetubes, strips the roller clean so that the powder material falls to thesurface below.

When discharge tubes 80 and 81 are energized, potential gradients arecreated surrounding the tubes which in turn ionize some of the airmolecules in the vicinity of the discharge tube. This effect is known ascorona. The ionized particles having the same polarity as that appearingin the surface of the discharge tube stream away from the dischargetubes creating air currents referred to as electronic winds. Theseelectronic winds are in a generally downward direction in the areabeneath dispensing roller 11. The downwardly directed electronic windand the electrostatic attraction of the powder particles, assist theforces of gravity in removing the particles from the roller. A largenumber of the released particles become charged with the same polarityas the surrounding air molecules. This effect creates a powder cloudbeneath the dispensing roller and brings about a more uniform dispersionof powder particles than could otherwise be achieved.

As previously mentioned, the dispensing rate is determined by therotational speed of dispensing roller 11, and the blade pressure againstthe dispensing roller surface. It should be noted that the Wiping bladeis relatively narrow and that the retaining member, which controls theblade pressure, is relatively close to the dispensing roller. With thisarrangement the blade pressure can be controlled with considerableaccuracy. Furthermore, since the adjusting screws are individuallyadjustable, the blade pressure can be adjusted separately in differentselected areas.

After the powder sprayer unit is placed in operation, the powderdistribution is observed and the roller speed and blade pressure areadjusted until a desired dispensing rate is achieved. If the powderdistribution is uneven, as may be caused by inaccuracies in thedispensing roller or side panels or by uneven wear, this is easilycorrected by adjusting the blade pressure in appropriate selected areas.In cases where a particular uneven distribution is desired, for example,more powder in the center than at the ends, such uneven distribution canbe attained by adjusting the blade pressure so that it is greater at theends than at the center.

The position of the discharge tubes can be adjusted so that one or bothof the tubes are effective, and hence, the effective strength of theelectrostatic field can be varied over a relatively wide range. Also,the tube position can be adjusted to provide an electrostatic fieldwhich is non-symmetrical and which thus tends to propel powder particlesin other than 21 directly downward direction. The non-symmetrical fieldcan be used, for example, the compensate for the effect of ambient aircurtains on the powder particles as they fall from the dispensing rollerto the surface below.

When the unit is placed in operation, a pneumatic pressure is created inthe plenum chambers by means of a suitable air pump to thereby create anair curtain on each side of the roller. These air curtains extendbetween the side panels and the surface below and thereby protect theenclosed area from ambient air currents.

Although only a few illustrative embodiments of the invention have beendescribed in detail, it should be obvious to persons skilled in the artthat there are numerous additional variations and embodiments within thescope of this invention. This invention is more particularly defined inthe appended claims.

What is claimed is:

1. In an electrostatic powder sprayer, the combination of a pair ofspaced apart end members;

receptacle means located between said end members forming a receptaclefor powder materials to be dispensed;

a metering mechanism including a dispensing roller journaled betweensaid end members and located in an opening beneath said receptacle, and

at least one Wiping blade secured to said receptacle means and disposedto tangentially engage said roller;

means for providing an electrostatic field at the surface of saiddispensing roller including a pair of electrostatic tubes parallel tosaid roller; positioning means for said pair of electrostatic tubes toposition said tubes 7 below said receptacle means,

closely adjacent said dispensing roller, substantially closer to saidroller than the receiving surface for the powder materials beingdispensed, and

on opposite sides of said metering mechanism;

high voltage alternating current energizing means connected to saidelectrostatic tubes to energize the same and create alternatingelectrostatic fields to free powder material from said dispensingroller,

to disperse the powder material and to at least partially control thedirection of the dispersed powder leaving said metering mechanism; and

pneumatic means secured to said receptacle means on each side of saidmetering mechanism and outside said electrostatic tubes for providingdownwardly directed air jets to create a pair of air curtains tending toconfine the dispensed powder material to a desired area beneath saidroller.

2. An electrostatic powder sprayer in accordance with claim 1 whereinsaid positioning means is adjustable to position said electrostatictubes to various positions closely adjacent and parallel to saiddispensing roller.

3. In an electrostatic powder sprayer, the combination of a pair ofspaced apart end members;

receptacle means located between said end members forming a receptaclefor powder materials to be dispensed;

a metering mechanism including a dispensing roller journaled betweensaid end members and located in an opening beneath said receptacle, and

a pair of wiping blades disposed to tangentially engage said dispensingroller so that one of said blades and said roller form a meteringmechanism;

a pair of electrostatic tubes parallel to said dispensing roller;

high voltage energizing means connected to said tubes to energize thesame and create electrostatic fields; positioning means coupled to eachof said tubes for positioning said tubes sufficiently close to saiddispensing roller to free powder particles from said roller andthereafter disperse the same, said tubes being positioned substantiallycloser to said roller than the receiving surface for the powdermaterials being dispensed; and

for positioning said tubes on opposite sides of said metering mechanismto at least partially control the direction of powder particles leavingsaid dispensing mechanism.

(References on following page) 1 1 References Cited UNITED STATESPATENTS 2,027,307 1/ 1936 Schacht. 2,027, 308 1/ 19 3 6 Schacht.2,394,657 2/1942 Beregh.

12 3,114,482 12/1963 Dunaway 322328 3,221,938 12/1965 Yonkers et a1.317262 X MILTON O. HIRSHFIELD, Primary Examiner.

Q J. A. SILV'ERMAN, Assistant Examiner.

1. IN AN ELECTROSTATIC POWDER SPRAYER, THE COMBINATION OF A PAIR OFSPACED APART END MEMBERS; RECEPTACLE MEANS LOCATED BETWEEN SAID ENDMEMBERS FORMING A RECEPTACLE FOR POWDER MATERIALS TO BE DISPENSED; AMETERING MECHANISM INCLUDING A DISPENSING ROLLER JOURNALLED BETWEEN SAIDEND MEMBERS AND LOCATED IN AN OPENING BENEATH SAID RECEPTACLE, AND ATLEAST ONE WIPING BLADE SECURED TO SAID RECEPTACLE MEANS AND DISPOSED TOTANGENTIALLY ENGAGE SAID ROLLER; MEANS FOR PROVIDING AN ELECTROSTATICFIELD AT THE SURFACE OF SAID DISPENSING ROLLER INCLUDING A PAIR OFELECTROSTATIC TUBES PARALLEL TO SAID ROLLER; POSITIONING MEANS FOR SAIDPAIR OF ELECTROSTATIC TUBES TO POSITION SAID TUBES BELOW SAID RECEPTACLEMEANS, CLOSELY ADJACENT SAID DIPENSING ROLLER, SUBSTANTIALLY CLOSER TOSAID ROLLER THAN THE RECEIVING SURFACE FOR THE POWDER MATERIALS BEINGDISPENSED, AND ON OPPOSITE SIDES OF SAID METERING MECHANISM; HIGHVOLTAGE ALTERNATING CURRENT ENERGIZING MEANS CONNECTED TO SAIDELECTROSTATIC TUBES TO ENERGIZE THE SAME AND CREATE ALTERNATINGELECTROSTATIC FIELDS TO FREE POWDER MATERIAL FROM SAID DISPENSINGROLLER, TO DISPERSE THE POWDER MATERIAL AND TO AT LEAST PARTIALLYCONTROL THE DIRECTION OF THE DISPERSED POWDER LEAVING SAID METERINGMECHANISM; AND PNEUMATIC MEANS SECURED TO SAID RECEPTACLE MEANS ON EACHSIDE OF SAID METERING MECHANISM AND OUTSIDE SAID ELECTROSTATIC TUBES FORPROVIDING DOWNWARDLY DIRECTED AIR JETS TO CREATE A PAIR OF AIR CURTAINSTENDING TO CONFINE THE DISPENSED POWDER MATERIAL TO A DESIRED AREABENEATH SAID ROLLER.